The present invention relates to improvements in plastic film bags with pressure closable and reopenable rib and groove profile fasteners at the top.
In the development of thin plastic film bags, an objective to be served is to provide a bag which has pressure closable and reopenable continuous rib and groove fastener elements at the top. Such fastener elements must securely close the bag and resist accidental opening due to forces on the side walls of the bag which occur during stacking, handling and merchandising. In order to reduce the cost of the bag, the fastener profiles are made as lightweight as possible without jeopardizing the facility of the fasteners to hold the bag closed. The ability of the fastener to remain closed can be augmented by design of a fastener but also by design of the bag structure in relation to the fastener structure. Coaction between the bag wall panels and the fastener strips can be attained by structural design so that stresses and pulls on the bag wall, such as occur inadvertently, do not pull apart the fastener strips to open the rib and groove profile fastener elements.
Efforts which have been made to provide a bag with a reclosable rib and groove fastener that withstands shocks and opening stresses have largely been directed at improving the form of the fastener, and in some instances it has been recognized that with a given fastener, the manner in which the forces are transmitted to the fastener is significant in improving the closure strength and integrity of the fastener strips. For example, an early development wherein a hinge action is sought so that the side wall of a bag can pivot outwardly without directly applying a stress to the fastener is shown and described in U.S. Pat. No. 3,054,434, Ausnit et al, entitled "Bag Closure". In this patent, a hinge arrangement is provided wherein the fastener strips are located at the top of the bag projecting fully above the bag walls.
Another form of structure provided to improve the closure strength is shown and describe in U.S. Pat. No. 3,347,298, Ausnit et al, entitled "Flexible Fastener With Unidirectional Opening Wherein Strengthening Filling Material is Utilized With the Fastener".
Another arrangement wherein some hinge relationship occurs between the side walls and the fastener is illustrated in U.S. Pat. No. 4,682,366, Ausnit et al, entitled "Attachment of Plastic Zipper to Incompatible Bag Wall Web", although the primary purpose of the disclosure is for other objectives.
An arrangement illustrating the use of a separate fastener attached within the walls of the bag is illustrated in co-pending application, Ser. No. 164,970, Van Erden, entitled "Bag With Separate Attachment Zipper and Method of Making", filed Mar. 7, 1988.
An object of the invention is to provide an improved bag structure which has a greater resistance to opening wherein the bag is constructed with separate fastener strips attached to the inner wall surface of the panels.
A further object of the present invention is to provide an improved bag construction and a method of making wherein the bag has a reclosable fastener at the top and can withstand pulls and stresses caused by the contents acting on the side walls of the bag without accidental opening of the bag.
A further object of the invention is to provide an improved structure and method of making the structure wherein a flexible bag is provided with a rib and groove type of reopenable fastener at the top and providing a structure wherein forces that tend to pull the bag open from inside the bag are applied to the rib and groove fastener in a shear mode rather than a peel mode so that the fastener resists accidental opening.